i'm going to give you a run down on the best unicycles to learn on, up to a high quality unicycle built for tricks and huge jumps.

starting off, a cheap unicycle will get the job done. it will allow for learning and a beginning at learning tricks(for those who wish to do so).

going from the best option to the worst as far as quality goes

~$110Torker LX is a common, all around good learning unicycle, i suggest it to any learner planning to do tricks because of the handle.

~$100
the Sun unicycles are good for people learning, very comparable to any other off brand cycle.

$???
schwinn makes a high quality unicycle, but they are meant to stay on the ground, and in my opinion are unreasonably priced

$60+
there are also many off brand and unbranded models of unicycles. they are fine to learn on, but will be beat up farily easily. they are also more likely to bend on a small drop than the LX

the CX is a great learner unicycle for SMALL children. i would suggest NOT getting it for anyone over the age of 10. the seat is ... well it is horrible. you don't want to get stuck with it.

Trick unicycles.
(all named are ISIS)

$$ EMAIL AEBIKE.com for the best price... $500 on unicycle.com much cheaper on AE bike.

Kris holm- definitely a very strong unicycle, the best (koxx unicycles are the same strength). i have beaten mine above and beyond what i expect any unicycle to hold up to, and it has held up quite well.
lightest because of it's aluminum frame

~$460~1000
Koxx one- comparable to the KH, but with many options, too many to mention... the most reasonable unicycle (my price and strength comparison) to get is the street unicycle with the street undrilled rim.
slightly heavier than the Kh

quax- the strongest stock unicycle, but heavy
these things are beasts. thats all that can be said about them, very few people regret buying a quax.

$255
$310 with crank upgrade
nimbus street ISIS- the best buy
comparable weight to the Koxx, just as stong, way cheaper. this unicycle is great for advancing riders, its shortcomings are the cranks and rim. the rim is slightly skinnier than it could be, and the cranks are cheesy compared to the KH cranks.
this is by far the best unicycle for price/strength when upgraded to KH cranks.

(NON ISIS)
$250
torker DX

outdated
heavy
but definitely strong
this is a good unicycle to buy used.
lifetime warranty on the frame... only one that has it.

quax- the strongest stock unicycle, but heavy
these things are beasts. thats all that can be said about them, very few people regret buying a quax.

very true. i think that the 48 spoke wheel is WAY overkill...at least for me at 100 lbs. i upgraded to a nimbus wheelset (it was when it was $86) mainly for ISIS ( i have the older qu-ax b4 they had ISIS) and i do some 4-6 ft drops and that 36spke wheel has barely budged.

the new qu-axs may be lighter with the isis axle and also they are more compatable w/ cranks.